how to set busy state while loading metadata

I'm working on a master-detail app which uses flexColumnLayout. I want to add busy handling according to the guideline (https://ux.wdf.sap.corp/fiori-design-web/busy-handling/): set page busy while loading metadata and not busy after loading. I have no idea inside which function to call setBusy(). Do you have any idea?

I want to set the whole page busy when I start the app, and set it free after the odata metadata is loaded.The metadata request is called automatically. It's not the same as the odata regular call which you know where you call it.

For the second party, maybe I would need to know why you want to wait for the metadata call. Usually, inside the metadata, you don't have real data but only metadata, so the user is not served with something to show.

The scenario is: "First, the UI description and metadata are loaded. This is the minimum for a basic functional UI. Until this data is available, the app UI needs to be blocked. Once the metadata has been loaded, we can partially unblock the UI where it makes sense. The busy state is set for the master list and the details area until the data has been loaded. Once the data for the master list area is available, the busy state is removed. Because the data for the details area is loaded asynchronously, its busy state is set separately."